There are many applications in which fasteners are used to join various parts of a device, machine, or vehicle together during the manufacturing process. One field where this is particularly important is the aircraft or airline industry. For example, fasteners may be used to mechanically join the outer skin of an aircraft to the subassembly. In some instances, the fasteners may be made of an aluminum alloy (e.g., 2017 or 2117). The exterior of most aircraft are made primarily of metal material, particularly aluminum and titanium.
A popular fastener to join most panels (e.g., metal panels) that make up, for example, the body of an aircraft are rivets. The exposed surface of such fasteners must meet corrosion resistance standards mandated by aircraft manufacturers.
Aluminum alloy fasteners may be treated (e.g., solution heat-treated, aged, coated, etc.) to attain certain physical and/or mechanical properties. For example, some aluminum alloy fasteners may be coated with an Alodyne coating to protect the base metal against corrosion damage.
The physical and mechanical properties of various aluminum alloys (e.g., 2017 and 2117) may be different. Thus, fasteners (e.g., rivets) made from these various materials will likewise be different. For example, a 2117 rivet is approximately 25 percent softer than a 2017 rivet. The method used to distinguish, for example, a 2117 rivet from a 2017 rivet is to place an indented dimple on the head of the 2117 fastener. Despite the use of this identification technique, cases in aircraft manufacturing have been documented where the softer 2117 fastener has been installed where the harder 2017 fastener should have been installed. Once this mistake is discovered a costly replacement program must be undertaken to drill out the softer 2117 alloy and replace it with the correct stronger 2017 alloy. If the mistake goes undiscovered, the damages could add up to the millions of dollars or the worst case situation, in human casualties. One solution proposed by aircraft manufacturers to this identification problem is to color code rivets for a specific user. For example, one aircraft manufacturer mandates that a 2117 rivet used to mechanically join the outer skin of an aircraft to the wing attachment subassembly be dyed orange. Unfortunately, it is often difficult to maintain the corrosion resistance properties of a dyed rivet, particularly in the case of a 2117 orange dyed rivet.
It is also difficult to achieve acceptable paint adhesion of subsequently applied paint to a dyed rivet. To target rivets having perceived acceptable corrosion resistance and/or paint adhesion, standards on the shade of the dye on the rivet have been implemented. Unfortunately, with conventional dye materials and procedures, these standards have proved difficult to meet.